1. Field of the Invention
The present invention relates to an alternate striped electrode array comprising first and second striped electrode arrays, where the first striped electrode array includes a plurality of first linear electrodes, the second striped electrode array includes a plurality of second linear electrodes alternating with the plurality of first linear electrodes, the plurality of first linear electrodes are transparent to a predetermined type of electromagnetic radiation, the plurality of second linear electrodes are opaque to the predetermined type of electromagnetic radiation, and the plurality of first linear electrodes and the plurality of second linear electrodes are arranged approximately parallel to each other. The present invention also relates to a process for producing the above alternate striped electrode array.
2. Description of the Related Art
In a conventionally known, radiographic-image recording method used in medical radiography and the like for reduction of patient exposure doses, improvement of diagnostic performance, and the like, a solid-state radiographic-image detector which functions as an electrostatic recording medium and includes a charge storage portion and a photoconductor (such as a selenium plate) sensitive to a radiation such as X rays is exposed to X rays carrying information on a radiographic image so that an amount of electric charges corresponding to an exposure dose of the X rays is stored in each area of the solid-state radiographic-image detector, i.e., the information on the radiographic image is recorded in the solid-state radiographic-image detector as a latent image. The information on the radiographic image recorded in the solid-state radiographic-image detector can be read by scanning the solid-state radiographic-image detector with a laser beam or a line-shaped light band. The above method is disclosed in the U.S. Pat. No. 4,535,468 and other publications.
The Japanese Unexamined Patent Publication No. 2000-284056 discloses a solid-state radiographic-image detector which concurrently realizes quick response and efficient readout of signal charges in the reading operation. The solid-state radiographic-image detector is constructed by forming a first electrode layer, a recording-side photoconductive layer, a charge storage portion, a reading-side photoconductive layer, and a second electrode layer in this order. The first electrode layer is transparent to recording light, which is a radiation or light emitted from excited states caused by a radiation. The recording-side photoconductive layer exhibits conductivity when the recording-side photoconductive layer is exposed to the recording light which has passed through the first electrode layer. Each area of the charge storage portion stores as latent-image charges an amount of electric charges corresponding to an exposure dose of the recording light in the area of the recording-side photoconductive layer corresponding to the area of the charge storage portion.
The reading-side photoconductive layer exhibits conductivity when the reading-side photoconductive layer is exposed to reading light. The reading-side photoconductive layer exhibits conductivity when the reading-side photoconductive layer is exposed to reading light. The second electrode layer comprises first and second striped electrode arrays, where the first striped electrode array includes a plurality of first linear electrodes, the second striped electrode array includes a plurality of second linear electrodes alternating with the plurality of first linear electrodes, the plurality of first linear electrodes are transparent to the reading light, the plurality of second linear electrodes are opaque to the reading light, and the plurality of first linear electrodes and the plurality of second linear electrodes are arranged approximately parallel to each other.
When the solid-state radiographic-image detector is irradiated with recording light which has passed through an object, the recording light enters the recording-side photoconductive layer through the first electrode layer, and generates first pairs of opposite (positive and negative) charges in each area of the recording-side photoconductive layer, where the amount of the first pairs of opposite charges generated in each area of the recording-side photoconductive layer corresponds to an exposure dose of the recording light in the area of the recording-side photoconductive layer. In the situation in which a negative voltage is applied to the first electrode layer and a positive voltage is applied to the second electrode layer, the negative charges generated in each area of the recording-side photoconductive layer is stored in the corresponding area of the charge storage portion as latent-image charges. Thus, a radiographic image of the object is recorded in the solid-state radiographic-image detector as a latent image. In particular, in the case where the first and second striped electrode arrays are connected at the time of the recording, the latent-image charges stored in each area of the charge storage portion are collected in the positions corresponding to the linear electrodes of the first and second striped electrode arrays.
Thereafter, when the reading-side electrode layer is scanned with the reading light, the reading light enters the reading-side electrode layer through the plurality of first linear electrodes constituting the second electrode layer, and generates second pairs of opposite charges in the reading-side photoconductive layer, and positive charges out of the second pairs of opposite charges are combined with the latent-image charges stored in the charge storage portion. On the other hand, negative charges out of the second pairs of opposite charges are combined with positive charges held in the first and second striped electrode arrays, so that the latent-image charges can be read out from the solid-state radiographic-image detector.
That is, in the solid-state radiographic-image detector disclosed in the Japanese Unexamined Patent Publication No. 2000-284056, transport charge having the opposite polarity to that of the latent-image charges can be held in the second striped electrode array as well as the first striped electrode array. Therefore, the amount of signal charges which can be read out from the solid-state radiographic-image detector can be increased, and thus the reading efficiency can be improved.
In order to produce the above solid-state radiographic-image detector disclosed in the Japanese Unexamined Patent Publication No. 2000-284056, it is necessary to produce an alternate striped electrode array comprising first and second striped electrode arrays which are made of different materials in such a manner that the linear electrodes constituting the first striped electrode array and the linear electrodes constituting the second striped electrode array are arranged alternately and approximately parallel to each other. An easily conceivable technique used for producing the above alternate striped electrode array is photolithography. In this case, the alternate striped electrode array can be produced by using at least two masks respectively provided for the first and second striped electrode arrays.
However, the size of the above solid-state radiographic-image detector is as large as 43 cmxc3x9743 cm. Therefore, in order to produce the alternate striped electrode array of the solid-state radiographic-image detector by photolithography, a large-sized exposure system which can realize high-precision mask alignment in a large area is required. In addition, in the case where more than one solid-state radiographic-image detector is concurrently manufactured by using a single exposure system for cost reduction, a larger-size exposure system is required. If only one solid-state radiographic-image detector is concurrently manufactured, the yield rate decreases, and the manufacturing cost and variations in the characteristics of the solid-state radiographic-image detectors increase.
Further, in the operation of reading the latent-image charges from the solid-state radiographic-image detector, one of the first and second striped electrode arrays is maintained at a reference potential, and the other of the first and second striped electrode arrays is connected to a current detection amplifier or the like. However, if there are variations in the (reference) potentials of the linear electrodes constituting the one of the first and second striped electrode arrays, the electric signals representing the latent-image charges read out from the solid-state radiographic-image detector are affected by the variations.
In order to eliminate the above variations in the reference potentials of the linear electrodes constituting one of the first and second striped electrode arrays, the one of the first and second striped electrode arrays can be formed as a common electrode. However, in this case, a further manufacturing process is required for connecting the linear electrodes constituting the one of the first and second striped electrode arrays.
An object of the present invention is to provide a process for producing an alternate striped electrode array in a self-aligned manner (without mask alignment) using only one mask designed for a single striped electrode array, without using a large-sized exposure system which can realize high-precision mask alignment in a large area, so as to enable multiple production (concurrent production of a plurality of alternate striped electrode arrays), yield rate improvement, and cost reduction.
Another object of the present invention is to provide an alternate striped electrode array which comprises first and second striped electrode arrays, and does not cause variations in electric potentials of linear electrodes constituting one of the first and second striped electrode arrays.
(I) According to the first aspect of the present invention, there is provided a process for producing an alternate striped electrode array which comprises first and second striped electrode arrays formed on a base transparent to a predetermined type of electromagnetic radiation, where the first striped electrode array includes a plurality of first linear electrodes, the second striped electrode array includes a plurality of second linear electrodes alternating with the plurality of first linear electrodes, the plurality of first linear electrodes are transparent to the predetermined type of electromagnetic radiation, the plurality of second linear electrodes are opaque to the predetermined type of electromagnetic radiation, and the plurality of first linear electrodes and the plurality of second linear electrodes are arranged approximately parallel to each other. The process comprises the steps of: (a) forming the second striped electrode array on an upper surface of the base; (b) forming a continuous, transparent conductive film on an upper surface of the base and an upper surface of the second striped electrode array; (c) forming a continuous resist film on an upper surface of the transparent conductive film, where the continuous resist film is negative with respect to the predetermined type of electromagnetic radiation; (d) forming a resist pattern corresponding to the second striped electrode array by applying the predetermined type of electromagnetic radiation through a lower surface of the base to the continuous resist film other than portions of the continuous resist film which are masked by the second striped electrode array; and (e) etching the transparent conductive film by using the resist pattern as a mask so that a portion of the transparent conductive film which remains after etching is separated from the second striped electrode array and forms the first striped electrode array.
In the steps (b) and (c), the meaning of the word xe2x80x9ccontinuousxe2x80x9d is that the transparent conductive film and the resist film include substantially no discontinuity or crevice. The surfaces of the transparent conductive film and the resist film are not necessarily flat, and the thicknesses of the transparent conductive film and the resist film are not necessarily uniform.
In addition, the transparent conductive film is formed on a partial or entire upper surface of the structure formed in the step (a). For example, the transparent conductive film may be formed on the upper surface of the structure formed in the step (a) other than the area including contacts of the plurality of second linear electrodes.
In the step (e), the etching is performed so that the first striped electrode array constituted by the portion of the transparent conductive film which remains after the etching is physically separated and electrically insulated from the second striped electrode array.
When the process according to the first aspect of the present invention is used, an alternate striped electrode array can be produced in a self-aligned manner (without mask alignment) using only one mask designed for a single striped electrode array, without using a large-sized exposure system which can realize high-precision mask alignment in a large area.
In addition, multiple production (concurrent production of a plurality of alternate striped electrode arrays) becomes possible, so that the yield rate can be improved and the manufacturing cost can be reduced.
Further, in the process according to the first aspect of the present invention, the first striped electrode array can be formed as a common electrode in which the plurality of first linear electrodes are connected at their ends on one side, without a specific manufacturing step for connecting the plurality of first linear electrodes. That is, the manufacturing cost can also be reduced in this sense.
(II) According to the second aspect of the present invention, there is provided a process for producing an alternate striped electrode array which comprises first and second striped electrode arrays formed on a base transparent to a predetermined type of electromagnetic radiation, where the first striped electrode array includes a plurality of first linear electrodes, the second striped electrode array includes a plurality of second linear electrodes alternating with the plurality of first linear electrodes, the plurality of first linear electrodes are transparent to the predetermined type of electromagnetic radiation, the plurality of second linear electrodes are opaque to the predetermined type of electromagnetic radiation, and the plurality of first linear electrodes and the plurality of second linear electrodes are arranged approximately parallel to each other. The process comprises the steps of: (a) forming the second striped electrode array on an upper surface of the base; (b) forming a continuous, transparent insulation film on an upper surface of the base and an upper surface of the second striped electrode array; (c) forming a continuous, transparent conductive film on an upper surface of the transparent insulation film; (d) forming a continuous resist film on an upper surface of the transparent conductive film, where the continuous resist film is negative with respect to the predetermined type of electromagnetic radiation; (e) forming a resist pattern corresponding to the second striped electrode array by applying the predetermined type of electromagnetic radiation through a lower surface of the base to the continuous resist film other than portions of the continuous resist film which are masked by the second striped electrode array; and (f) etching the transparent conductive film by using the resist pattern as a mask so that a portion of the transparent conductive film which remains after etching forms the first striped electrode array.
In the steps (b), (c), and (d), the meaning of the word xe2x80x9ccontinuousxe2x80x9d is that the transparent insulation film, the transparent conductive film, and the resist film include substantially no discontinuity or crevice. The surfaces of the transparent insulation film, the transparent conductive film, and the resist film are not necessarily flat, and the thicknesses of the transparent insulation film, the transparent conductive film, and the resist film are not necessarily uniform.
In addition, the transparent insulation film is formed on a partial or entire upper surface of the structure formed in the step (a). For example, the transparent insulation film may be formed on the upper surface of the structure formed in the step (a) other than the area including contacts of the plurality of second linear electrodes.
Further, the transparent conductive film is formed on a partial or entire upper surface of the structure formed in the step (b).
The transparent insulation film is transparent to the above predetermined type of electromagnetic radiation, and provided for electrically insulating the second striped electrode array and the first striped electrode array made of the transparent conductive film, from each other.
It is preferable to perform heat treatment for realizing thermal contraction of the resist pattern in the structure formed in the step (e), before performing the operation in step (f). When the heat treatment is performed, it is possible to efficiently realize underetching, which is explained later.
The process according to the second aspect of the present invention has the same advantages as the process according to the first aspect of the present invention. In addition, it is possible to further improve the insulation performance.
(III) According to the third aspect of the present invention, there is provided a process for producing an alternate striped electrode array which comprises first and second striped electrode arrays formed on a base transparent to a predetermined type of electromagnetic radiation, where the first striped electrode array includes a plurality of first linear electrodes, the second striped electrode array includes a plurality of second linear electrodes alternating with the plurality of first linear electrodes, the plurality of first linear electrodes are transparent to the predetermined type of electromagnetic radiation, the plurality of second linear electrodes are opaque to the predetermined type of electromagnetic radiation, and the plurality of first linear electrodes and the plurality of second linear electrodes are arranged approximately parallel to each other. The process comprises the steps of: (a) forming a continuous, transparent conductive film on an upper surface of the base; (b) forming the second striped electrode array on an upper surface of the transparent conductive film; (c) forming a continuous resist film on an upper surface of the transparent conductive film and an upper surface of the second striped electrode array; (d) forming a resist pattern corresponding to the second striped electrode array by applying the predetermined type of electromagnetic radiation through a lower surface of the base to the continuous resist film other than portions of the continuous resist film which are masked by the second striped electrode array; (e) producing gaps between the resist pattern and the second striped electrode array so as to expose the transparent conductive film at bottoms of the gaps; and (f) etching the transparent conductive film by using the resist pattern and the second striped electrode array as a mask so that a portion of the transparent conductive film which remains after etching is separated from the second striped electrode array and forms the first striped electrode array.
In the steps (a) and (c), the meaning of the word xe2x80x9ccontinuousxe2x80x9d is that the transparent conductive film and the resist film include substantially no discontinuity or crevice. The surfaces of the transparent conductive film and the resist film are not necessarily flat, and the thicknesses of the transparent conductive film and the resist film are not necessarily uniform.
In addition, the transparent conductive film is formed on a partial or entire upper surface of the structure formed in the step (b). For example, the transparent conductive film may be formed on the upper surface of the structure formed in the step (b) other than the area including contacts of the plurality of second linear electrodes.
The operation in step (e) may be any operation which can produce gaps between the resist pattern and the second striped electrode array and expose the transparent conductive film at bottoms of the gaps so as to enable etching of the transparent conductive film. For example, the operation in step (e) may be realized by the aforementioned heat treatment.
In the step (f), the etching is performed so that the first striped electrode array constituted by the portion of the transparent conductive film which remains after the etching is physically separated and electrically insulated from the second striped electrode array.
The process according to the third aspect of the present invention has the same advantages as the process according to the first aspect of the present invention.
(IV) The following features are common to the processes according to the first to third aspects of the present invention.
(i) The predetermined type of electromagnetic radiation is an electromagnetic radiation which can transmit through the transparent conductive film and to which the resist film is sensitive.
(ii) The transparent conductive film is not necessarily 100% transparent to the predetermined type of electromagnetic radiation. It is sufficient that the transparent conductive film is transparent to the predetermined type of electromagnetic radiation to such a degree that the resist film can be substantially exposed to the predetermined type of electromagnetic radiation which has passed through the transparent conductive film.
In addition, it is not necessary that the second striped electrode array completely stops the predetermined type of electromagnetic radiation. It is sufficient that the second striped electrode array stops the predetermined type of electromagnetic radiation to such a degree that substantially the resist film cannot be exposed to the predetermined type of electromagnetic radiation which has passed through the second striped electrode array.
(iii) The transparent conductive film is a film of which the first striped electrode array is formed, and is made of a material which is transparent to the predetermined type of electromagnetic radiation and so conductive that the material can be used for forming the first striped electrode array.
(iv) The etching may be such a type that underetching occurs. The underetching is a phenomenon in which etching proceeds in the horizontal direction as well as the vertical direction. For example, in the case of FIG. 5, etching proceeds from the edges of the resist pattern 18a in the horizontal direction as well as the vertical direction. Therefore, the portions of the transparent conductive film 16 located under the resist pattern 18a are removed by underetching. As a result of the underetching, each linear electrode 12a constituting the second striped electrode array is separated from the remaining portions of the transparent conductive film 16.
(v) Preferably, the transparent conductive film is made of a completely amorphous material.
If the transparent conductive film is made of a microcrystal material such as the conventional ITO films, the etching rate is likely to vary depending on the location in the transparent conductive film. Therefore, a short circuit may be formed where the etching rate is insufficient, and the first and second striped electrode arrays may be disconnected where the etching rate is excessively high. That is, when the transparent conductive film is made of a microcrystal material, it is not easy to construct an alternate striped electrode array having a large area and uniform characteristics in the large area.
The completely amorphous material is a material having a substantially complete amorphous structure. For example, the IZO (indium-doped zinc oxide) such as IDIXO (Idemitsu Indium X-metal Oxide) and the completely amorphous ITO produced by precisely adding H2O to sputtering gas are known as a completely amorphous material, where IDIXO is a kind of the IZO which is completely amorphous and manufactured by Idemitsu Kosan Co., Ltd. Alternatively, any other material having a completely amorphous structure can be used for forming the transparent conductive film.
In the case where the transparent conductive film is made of a completely amorphous material such as IDIXO, underetching can proceed at a uniform etching rate at every location in the transparent conductive film. In this case, deep underetching becomes possible. For example, the first striped electrode array can be separated from the second striped electrode array with a distance of 10 micrometers by underetching. In addition, since the edges of the first striped electrode array are smoothed, charge injection from the edges of the first striped electrode array can be reduced.
Further, it is possible to produce a completely amorphous ITO film by precisely adding H2O to sputtering gas. When the transparent conductive film is made of a completely amorphous ITO film, it is possible to make the first striped electrode array alkali resistant.
(vi) In the case where the underetching is used for separating the first and second striped electrode arrays from each other, it is necessary that the gaps formed between the first and second striped electrode arrays are sufficient to prevent formation of a short circuit between the first and second striped electrode arrays and occurrence of a harmful phenomenon such as noise production caused by interaction between the first and second striped electrode arrays. On the other hand, when the underetching proceeds too much, a small flaw in the transparent conductive film can be extended to such a degree that a defect (e.g., a disconnection in the first and second striped electrode arrays) is produced.
Specifically, it is preferable that the gaps between the first and second striped electrode arrays are within the range from 1 to 7 micrometers. More preferably, the gaps are within the range from 2 to 5 micrometers. When the gaps are within the above ranges, it is possible to prevent formation of a short circuit between the first and second striped electrode arrays, occurrence of a harmful phenomenon (such as noise production) caused by interaction between the first and second striped electrode arrays, and production of a harmful defect (such as a disconnection) caused by excessive underetching.
(V) According to the fourth aspect of the present invention, there is provided an alternate striped electrode array comprising: a base which is transparent to a predetermined type of electromagnetic radiation; a first striped electrode array being formed above the base and including a plurality of first linear electrodes which are transparent to the predetermined type of electromagnetic radiation; and a second striped electrode array being formed above the base and including a plurality of second linear electrodes which are opaque to the predetermined type of electromagnetic radiation and alternate with said plurality of first linear electrodes. The plurality of first linear electrodes and the plurality of second linear electrodes are arranged approximately parallel to each other, and the plurality of first linear electrodes are connected at their ends on one side so as to form a common electrode.